This is a very good idea.

The issue with the reviews is that there are not enough of them. With many (most?) modules it isn't just a matter of "not enough to determine quality" - there aren't any!

CPAN won't see a great volume of reviews without serious thinking and work going into the review system. Which is why I like your idea: it is simple, and gets the job done. If even a few reviews that said "This module is a 4/5, it does X well but if you want to do Y too you should look at module Z" it would help me track down my best-fit module faster.

I think I'll start adding reviews like this when I find a set of good, related solutions.